Overall survival for patients with advanced stage pancreatic cancer has remained largely unchanged in the 11 years since the approval of gemcitabine. The recent failures of oxaliplatin, bevacizumab, or cetuximab to improve survival have prompted NCI's GI Cancer Steering Committee to call on investigators to evaluate novel therapeutic approaches to find new exploitable targets in this disease. There is provocative evidence that the vitamin D pathway may be one such target. The vitamin D receptor (VDR) is overexpressed in the vast majority of human pancreatic cancers and exposure to vit D reduces in vitro cell proliferation rates through key pathogenetic mechanisms including matrix metalloproteinases, E-cadherin and 2-catenin. Individuals with the highest vit D levels have a 20-40% lower incidence of pancreatic cancer. Prior attempts to administer vit D analogs on a daily basis in this disease have been limited by the development of dose-limiting hypercalcemia. DN-101 is a proprietary formulation of calcitriol that is administered on a weekly rather than a daily basis. Its improved bioavailability allows therapeutic plasma concentrations to be achieved without associated hypercalcemia. DN-101 potentiates the cytotoxicity of gemcitabine against pancreatic cancer cell lines and xenografts. Since the original submission of this grant, the principal investigator and sponsor have finalized the design and begun initiation of a 4-arm, randomized, placebo-controlled Phase IIB study in patients with advanced stage disease to evaluate gemcitabine + placebo; gemcitabine + DN-101; gemcitabine, erlotinib, and placebo; and gemcitabine, erlotinib, and DN-101. The primary clinical endpoint of the trial will be 6-month survival rate. The study will have 90% power to detect a true 6-month survival rate >50% in either of the investigational treatment arms. This revised R21 will support biological correlative studies in tumor and blood to elucidate the way(s) in which DN-101 may enhance the efficacy of systemic therapy. Our two specific aims are: 1) to determine whether baseline characteristics in the tumor and/or serum predict the clinical or biological effects of DN-101 in patients with advanced pancreatic cancer and 2) to determine whether changes in biological targets measurable in plasma and serum predict for or correspond to clinical outcomes in these patients. The studies for Specific Aim 1 will be performed on tissue obtained from the original diagnostic tissue to measure expression and localization of the vitamin D receptor, E-cadherin, 2-catenin, and p120. Studies for Specific Aim 2 will be performed on serial plasma or serum samples to measure changes in MMP-2 and -9, vit D metabolites, cytidine deaminase activity, CYP24 activity and PTH at specific time points during treatment. As requested by the reviewers, the power analysis for these studies have been clarified. We believe that the studies outlined in this revised application will provide important insights into biological mechanisms by which vitamin D may augment the activity of systemic therapy and lead to improved outcomes for patients with advanced pancreatic cancer. PUBLIC HEALTH RELEVANCE: DN101, a form of high-dose Vitamin D, is being evaluated in combination with chemotherapy in a clinical trial for people with advanced pancreatic cancer. This project will help us understand the biological mechanisms by which DN101 might enhance the activity of that chemotherapy. [unreadable] [unreadable] [unreadable]